We are investigating the biotransformation of foreign organic compounds in hepatic and extrahepatic tissues of vertebrate and invertebrate marine species from coastal Maine and Florida. Both cytochrome P-450-dependent monooxygenase activities and alkene and arene oxide-metabolizing enzymes (epoxide hydrolase and glutathione transferases) are being characterized in control fish and in fish pre-exposed to polycyclic aromatic hydrocarbons. Some studies are being undertaken with purified cytochrome P-450 and with purified glutathione transferases from aquatic species. Emphasis is given to projects that will enhance our understanding of toxication-detoxication mechanisms.